1. Field of the Invention
This invention relates to a data format conversion method and equipment for converting a data format such as a program to a different data format. More particularly, the invention relates to a data format conversion method and equipment suitable for a controller management system for managing a controller having an embedded computer (hereinafter called merely “computer”), particularly a controller management system for managing a controller from a remote place.
The term “program, etc.” used in this specification means programs and electronic information analogous to the programs. The term “program” means also directions to a computer that are so combined with one another as to acquire one result. The term “electronic information analogous to programs” means information that is used for processing by a computer. The term “data format” means formats of languages and description of programs and data structures. The term “management of controller” includes monitoring and management of a controller from a remote place through a communication network besides management such as preparation, edition, re-writing, etc, of programs of a computer embedded into the controller.
2. Description of the Related Art
Programmable controllers and programmable logic controllers (PLC) having an embedded computer (hereinafter called merely “controller”) have gained a wide application. When a program is installed or re-written to or in the computer of such a controller, it has been customary to connect a dedicated programmer unit to the embedded computer through cables and to transfer a program created by the dedicated programmer unit to the computer.
However, the functions of the dedicated programmer unit have quickly been antiquated due to innovation and progress of computer technologies, and it has become difficult to secure a dedicated programmer unit capable of coping with a variety of controllers. Some of the controllers for controlling infrastructure facilities have continuously been operated for a long term of 15 years or more, and management of such controllers must also be made for a long term. Conventionally, it has been necessary to secure in advance a dedicated programmer unit by estimating possible troubles so that the controllers can be managed for 15 years or more. Therefore, efficiency of cost and improvement of performance have left problems yet to be solved.
To solve such problems, JP-A-11-24716 (hereinafter called “prior art 1”) proposes a management system using personal computers (PC) excellent in versatility and cost performance and communication application technologies typified by the Internet. In this prior art 1, an HTTP (Hyper Text Transfer Protocol) server is mounted to a user controller and a programmer acquires HTML (Hyper Text Markup Language) data from the controller through a Web browser of the PC and controls the program of the controller in accordance with the HTML data so acquired.
To improve controller management efficiency, standardization of description languages of programs has been required. To satisfy this requirement, U.S. Patent Application Publication US2002/0004804A1 (hereinafter called “prior art 2”) proposes to describe a program by a markup language. In this prior art 2, XML (Extensible Markup Language) is picked up as an example of the markup languages, and a programmer unit converts a program created by an editor to an XML type program and transfers it to a controller. The controller stores the XML type program in its own memory device, interprets the program by control execution means inside the controller and controls a controlled target. Incidentally, XML is a data standard stipulated by W3C (World-Wide Web Consortium) as a standardization organization. The XML is expected to be a promising standard used for a long time as a data standard employed in networks.
On the other hand, JP-A-2001-350507 (hereinafter called “prior art 3”) discloses a technology for parsing data described in a markup language at a communication terminal having limited performance in connection with the communication terminal having a built-in browser for establishing an interface with people. In other words, a network interface is interposed in a route in which the communication terminal acquires data described by WML (Wireless Markup Language) from an HTTP server. The network interface includes WAP gateway means for converting a WML source acquired from the HTTP server to a content of compiled WML before the WML source is transmitted to the communication terminal. When a user of the communication terminal requires the WML information to the HTTP server, the network interface compiles the WML source and transmits the result to the communication terminal. In consequence, even the communication terminal having limited processing capacity can peruse the data described by the markup language.
On the other hand, computers connected to a communication network have been embedded to fields or products for which such application has not been possible in the past, due to the progress of semiconductor process technology and communication network technology. It is hereby of importance that such an embedded computer minimizes an operation cost. Therefore, the embedded computers generally have limited functions and less expansibility when they are embedded. In other words, the function of the computers is specified to a specific control before embedding. Services for executing control including monitoring irrespective of time and place have gradually become available by using such embedded computers in combination with a communication network and communication terminals.
However, problems have remained yet to be solved so as to program, monitor and control the embedded computers from the communication network. The controller management system proposed in the prior art 1 is not free from the problem that control is limited to the content of the HTML data stored in the controller.
To solve this problem, it may be possible to utilize a CGI (Common Gateway Interface) as one of the technologies for expanding the HTTP function, for example.
In this case, the HTTP server must have the CGI function as well as a sufficient processing capacity, but it is not realistic to furnish the embedded computer with the CGI function and the processing capacity. In addition, flexibility drops because the CGI program must be registered to the HTTP server whenever a necessary function is added. SSI (Server Side Include), JSP (Java (trademark) Server Page), and so forth, are available as the technology for expanding the server function besides the CGI but they involve the same problem.
On the other hand, the controller management system proposed in the prior art 2 uses a markup language as the program. Therefore, it is necessary to conduct a validation/validity check whether or not the data structure described is coincident with data definition. The validation/validity check is necessary particularly in the case of the XML. Since the XML is described by a text, the embedded computer cannot directly utilize the XML. Therefore, processing for extracting information that the embedded computer can utilize from the text description is necessary.
However, the processing of the types described above is temporary processing, and it is not desirable to improve a calculation processing capacity only for such a processing in the embedded computer for which the minimum operation cost is preferentially required. In the programmer unit, on the other hand, XML conversion means corresponding to each controller must be prepared, and the controller management system cannot easily cope with different kinds of controllers manufactured by different manufacturers.
In the gateway apparatus disclosed in the prior art 3, correspondence to the language compiled from the source is primarily determined.
As described above, the languages to which the controllers having a variety of embedded computers can correspond are individually determined. Therefore, development of a programmer unit having high flexibility and high versatility and capable of programming through a communication network, etc, has been desired for controllers having a variety of embedded computers.